Myeloproliferative Neoplasms

Myeloproliferative Neoplasms

Myeloproliferative Neoplasms

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MPN Overview & Classification - Proliferation Powerhouse

⭐ MPNs are clonal hematopoietic stem cell disorders characterized by proliferation of one or more myeloid lineages, often with a relatively mature phenotype.

  • Hallmark: Autonomous proliferation of myeloid cells.
  • WHO Classification (Major):
    • Chronic Myeloid Leukemia (CML): BCR-ABL1 positive.
    • Polycythemia Vera (PV): ↑ RBCs.
    • Essential Thrombocythemia (ET): ↑ Platelets.
    • Primary Myelofibrosis (PMF): Marrow fibrosis, splenomegaly.
    • Chronic Neutrophilic Leukemia (CNL)
    • Chronic Eosinophilic Leukemia, NOS (CEL, NOS)
  • Key Pathogenesis: Tyrosine kinase activation (e.g., JAK2 V617F, CALR, MPL).
  • Clinical: ↑ Blood counts, organomegaly, thrombosis/bleeding risk.

Chronic Myeloid Leukemia (CML) - Philly's Chromosome Tale

  • MPN: Dysregulated production of mature/maturing granulocytes.
  • Pathogenesis:
    • ⭐ > The Philadelphia chromosome, t(9;22)(q34.1;q11.2), resulting in the BCR-ABL1 fusion oncogene, is the pathognomonic molecular lesion in CML.
    • BCR-ABL1: Constitutively active tyrosine kinase.
  • Clinical Phases (📌 CAB):
    • Chronic: <10% blasts. Most common.
    • Accelerated: 10-19% blasts, basophilia ≥20%, worsening splenomegaly/cytopenias.
    • Blast Crisis: ≥20% blasts (myeloid/lymphoid). Like acute leukemia.
  • Diagnosis:
    • PBS: Marked leukocytosis, left shift, basophilia, eosinophilia.
    • BM: Hypercellular, ↑M:E ratio.
    • t(9;22) or BCR-ABL1 (Cytogenetics/FISH/PCR). CML Karyotype with t(9;22) and FISH Philadelphia chromosome OR CML peripheral blood smear with marked leukocytosis, left shift, basophilia)
  • Treatment:
    • Tyrosine Kinase Inhibitors (TKIs) e.g., Imatinib.

PV, ET, & PMF - The JAK/CALR/MPL Crew

⭐ JAK2 V617F mutation is the most common driver mutation in BCR-ABL1 negative MPNs, present in >95% of Polycythemia Vera cases and ~50-60% of Essential Thrombocythemia and Primary Myelofibrosis cases.

FeaturePolycythemia Vera (PV)Essential Thrombocythemia (ET)Primary Myelofibrosis (PMF)
Defining↑ RBC mass (Hb >16.5/16 g/dL), PanmyelosisSustained ↑ Platelets (≥450,000/μL), no reactive causeBM fibrosis, Extramedullary hematopoiesis (EMH), cytopenias
MutationsJAK2 V617F (>95%), JAK2 Exon 12JAK2 V617F (50-60%), CALR (25-35%), MPL (~5-10%)JAK2 V617F (50-60%), CALR (25-35%), MPL (~5-10%)
Key Labs↓ Serum EPO; ↑WBC, ↑Platelets often; ↑LDH, ↑Uric acidNormal/↑ EPO; Platelets ≥450,000/μLAnemia (often severe); Leukoerythroblastosis; Teardrop RBCs
Bone MarrowHypercellular (panmyelosis); Pleomorphic megakaryocytes↑ Megakaryocytes (large, staghorn clusters); No/minimal fibrosisFibrosis (reticulin/collagen); Dry tap; Osteosclerosis
ClinicalPlethora, aquagenic pruritus, splenomegaly, thrombosis, goutThrombosis/hemorrhage, erythromelalgia, mild/no splenomegalyMassive splenomegaly, B-symptoms, bone pain, cachexia
ProgressionMyelofibrosis (MF) (~10-15%), Acute Myeloid Leukemia (AML) (~2-5%)MF (<10%), AML (~1-2%)AML (~5-20%)

MPN Complications & Progression - Trouble Brewing

  • Thrombotic/Hemorrhagic Events: Arterial (MI, CVA), venous (DVT, PE); often due to abnormal platelet function or count.
  • Hyperuricemia & Gout: Result of ↑ cell turnover.
  • Progressive Splenomegaly: Common, from extramedullary hematopoiesis.
  • Disease Progression:
    • Myelofibrosis (Spent Phase / Post-PV/ET MF)
    • Acute Myeloid Leukemia (AML) transformation (poor prognosis)

⭐ The major long-term risks across MPNs include thrombotic and hemorrhagic events, progression to myelofibrosis (spent phase), and transformation to acute myeloid leukemia (AML).

High‑Yield Points - ⚡ Biggest Takeaways

  • JAK2 V617F mutation is a common driver in PV, ET, and PMF.
  • Polycythemia Vera (PV): ↑RBC mass, ↓EPO, and characteristic aquagenic pruritus.
  • Essential Thrombocythemia (ET): Marked thrombocytosis, with thrombotic/hemorrhagic risks.
  • Primary Myelofibrosis (PMF): Features bone marrow fibrosis, extramedullary hematopoiesis, and dacrocytes.
  • CML: BCR-ABL1 fusion (Philadelphia chromosome) is pathognomonic; treat with TKIs.
  • MPNs can transform to AML or progress to myelofibrosis (spent phase).
  • CALR and MPL mutations are significant in JAK2-negative ET/PMF.

Practice Questions: Myeloproliferative Neoplasms

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Flashcards: Myeloproliferative Neoplasms

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The size of M-BCR ABL (Major BCR) protein in t(9;22) associated with chronic myeloid leukemia (CML) is _____ kDa.

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The size of M-BCR ABL (Major BCR) protein in t(9;22) associated with chronic myeloid leukemia (CML) is _____ kDa.

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